The present invention relates to devices and methods for facilitating endovascular interventions, such as endovascular embolization of arteriovenous malformations (“AVMs”), arteriovenous fistulas (“AVFs”), angioplasty, and stenting, tumor embolization, and increased delivery of a therapeutic agent to targeted tissue.
Normal arterial and venous blood vessels connect to each other at the capillary level where blood flows at a relatively low rate and at a low pressure, which allows for the efficient transfer of nutrients, oxygen, and metabolic waste products between the blood and the body tissue. AVMs and AVFs, in contrast, are abnormal connections between arteries and veins at a level above the capillary level that occur in organs such as the brain. The abnormal connections provide a path of low resistance, which results in blood flow bypassing blood vessels at a vascular level lower than that where the abnormal connection occurs. The abnormal bypass may result in an ischaemic or hypoxic condition at least with respect to the tissue affected by the bypass. Moreover, the low resistance path provided by the malformation or fistula results in a relatively high blood flow rate through the malformation or fistula and at high pressure, which creates a risk of rupture that may result in a stroke or bleeding.
A variety of methods of treating AVMs and AVFs have been adopted. One approach has been to create an endovascular occlusion or embolization in the malformation or fistula by introducing a blocking material, such as a glue or polymer, typically in a liquid form via a catheter into the malformation or fistula. The liquid blocking material is typically introduced upstream of the AVM or AVF such that blood flow carries the blocking material downstream to the target site where the material sets to form the occlusion. This method of treating AVMS and AVFs, however, is prone to complications associated with the relative difficulty in performing the procedure. Introducing the blocking material upstream of the target, for instance, may result in the blocking material being carried away beyond or bypassing the abnormal connection to normal vasculature where the material will set to form unwanted embolisms that may result in a stroke with potentially catastrophic effects.
Arteriosclerosis (or, more properly, atherosclerosis) is the progressive narrowing and hardening of the arteries over time resulting from aging as well as other risk factors known to accelerate the process, such as high cholesterol, high blood pressure, smoking, diabetes, etc. Angioplasty, a common non-invasive method of treating such a stenosis, entails introducing a balloon-tipped catheter into the diseased blood vessel where the balloon is inflated to expand the blood vessel with the stenosis in order to improve blood flow through the vessel. Stenting has also been adopted as a method of treating a stenosis, either alone or in combination with angioplasty, particularly with respect to coronary and carotid arteries. Stenting entails introducing a stent, e.g., a device developed to keep the lumen of a blood vessel open, to maintain the patency of blood vessels. Endovascular procedures, such as angioplasty and stenting, however, typically cause embolic particles or plaque to dislodge from the site of the stenosis and pose a risk of distal embolisms. This is particularly problematic with arteries providing blood to the brain, such as the carotid artery.
Although chemotherapy treatments are designed to attack specific disease producing microorganisms or selectively destroy cancerous tissue, in practice the chemical treatment often has deleterious effects on normal tissue. Accordingly, in many instances the particular dosage for the chemotherapy treatment is a balance between the desire to eliminate the microorganism or cancerous tissue while limiting the damage to normal tissue. In this respect, the effectiveness of chemotherapy against the offending organism or tissue is limited by the potential harm to distal normal tissue.
Three noteworthy techniques and corresponding devices have been adopted in connection with carotid artery angioplasty and stenting to protect against distal embolisms: distal occlusion, distal filtration, and proximal occlusion. Although these techniques have proven to be necessary accompaniments, particularly with carotid artery angioplasty and stenting, the techniques have associated therewith a number of disadvantages, which are discussed below.
The distal occlusion technique entails expanding a balloon catheter downstream from the stenosis, which serves to block blood flow, which typically includes embolic particles dislodged during the angioplasty or stenting procedure, to the brain. The site of the angioplasty or stenting procedure is aspirated upon completion of the procures to remove the embolic particles from the site and the balloon catheter subsequently released so that normal blood flow through the carotid artery may be resumed. Distal occlusion, however, has a number of shortcomings. For instance, distal occlusion may not protect against embolic particles entering the blood stream and traveling to the brain via a patent carotid artery. Additionally, the procedure is relatively cumbersome, requiring the user to manipulate a number of endovascular tools, e.g., the blocking catheter, angioplasty catheter, aspiration catheter, etc., within the stenotic blood vessel. This problem is compounded particularly where the stenosis occurs in tortuous blood vessels or though which tortuous blood vessels the catheters must navigate to reach the stenosis.
The distal filtration technique entails placing a filtering medium via a catheter downstream from the stenosis in order to capture embolic particles that may be dislodged during the angioplasty or stenting procedures. Distal filtration, however, is similarly cumbersome and the filter medium is not capable of capturing particles smaller than the pore size of the filter medium. The filter medium may, in addition, thrombose, which may result in blood clots entering the blood stream, such as through a patent artery, posing a risk of a distal embolism.
Finally, proximal occlusion entails placing a blocking device upstream from the stenosis via a catheter to also block blood flow in the brain. Embolic particles dislodged during the angioplasty or stenting procedure are aspirated from the site, upon completion of the procedures, by temporarily reversing blood flow through the stenotic artery and draining the fluid from the site. Associated with proximal occlusion, however, is the potential for causing distinction or spasm in the artery.
Current methods for distal protection of normal tissue during embolization of a tumor include occlusion of the proximal vessel with a temporary or permanent agent. These methods are often unsatisfactory because collateral flow through the tumor often harms the normal tissue distal to the occlusion. Increasing the dose of a drug along with a partial embolization results in a breakdown of the blood brain barrier; however, these methods are difficult to control and may adversely affect non-target tissue.
There is therefore an ongoing need for methods and devices for facilitating endovascular interventions, such as the endovascular embolization, angioplasty, stenting, tumor embolization, etc., that reduce the risk of unwanted or distal embolisms. There is also a need for methods and devices for increasing the efficiency of targeted delivery of therapeutic agents to tissue.